1. Field of the Invention
The present invention relates to folding apparatuses, and more particularly to apparatuses for folding an edge on a continuous material web.
2. Description of Related Art
The material which is employed for disposable packages for liquid foods such as milk or juice normally consists of a paper or cardboard layer which is laminated on both sides with a thermoplastic. The laminate may occasionally also include a thin aluminium foil.
After production of the laminate, this is cut in suitable widths and formed into packages in a filling machine. The point of departure for this operation is that the packaging material supplied from a roll is formed into a tube which is transversely sealed and then cut in the transverse seals, in order finally to be formed into the finished package.
Since the longitudinal joint is sealed in that the two edges overlap one another so that the material web becomes a tube, the edge located inside the tube must be protected in some manner so that the filled contents do not come into direct contact with the paper layer in the laminate. Otherwise, this could result in the contents wetting the paper layer and, in aseptic packages or cartons, such a joint would give rise to a lack of sterility.
Normally, the inner longitudinal edge is protected by a loose strip which is sealed against the outer thermoplastic layer in the laminate. It is also possible, in production of the laminate, to allow a narrow edge of thermoplastic, possibly laminated with aluminium foil, to protrude outside the edge of the packaging material proper.
Such an edge of thermoplastic, possibly with adhering aluminium foil, must, before arrival of the packaging material at the filling machine, be folded over the open laminate edge in order thereby to protect this edge. This, this operation is presently carried out in a manner such that the edge is heated by hot air or by an IR lamp and is then folded by means of a number of rollers which are at different angles of inclination. Such an apparatus provides for adequate folding. However, friction is great and only limited output capacity is possible. Moreover, prior art apparatuses are also complex and contain many moving parts. Such an apparatus is described in U.S. Pat. No. 4,606,784.